The laser has developed into a very useful tool in modern surgery. Because of pinpoint accuracy and minimal peripheral thermal damage, the laser has found wide use in many areas of medicine. With the introduction of laser units with 25 to 100 watts power output, the carbon dioxide laser has begun to be used for excision and vaporization of tissue in neurosurgery and plastic surgery as well as gastroenterology, urology, otolaryngology, gynecology and, most recently, in cardiac applications.
Lasers are particularly useful in transmyocardial revascularization. Transmyocardial revascularization is a recently developed method for treating ischemic heart disease. Heart disease is the leading cause of disability and death in all industrialized nations, accounting for nearly twice as many deaths as those resulting from cancer. The majority of these deaths are due to ischemic heart disease, a condition in which the heart muscle or myocardium does not receive an adequate nutritive blood supply. Transmyocardial revascularization is a technique used to supplement the blood supply delivered to the heart by providing the ischemic inner surface (endocardium) direct access to blood within the ventricular chamber. Normally the endocardium does not have direct access to the ventricular chamber and receives its nutritive blood supply entirely from the coronary arteries branching through the heart wall from its outer surface (epicardium).
A carbon dioxide laser has been used in transmyocardial revascularization. In short, the laser was used to vaporize tissue from the epicardium through the endocardium to the ventricular chamber, thereby promoting the ischemic myocardium direct access to blood within the chamber.
Using the above technique creates several problems. The vaporized tissue at the heart's outer surface (epicardium) must be sutured to prevent copious blood loss due to the forceful pumping action of the ventricular cavity. This is time-consuming and clearly dangerous to the patient. Further, the focal point of the laser beam cannot be maintained as it proceeds from the epicardium through the endocardium. If the laser beam is focused at the epicardial surface, it will be unfocused mid-way through the heart wall. An unfocused CO.sub.2 laser beam does not precisely vaporize the tissue, but instead merely heats and coagulates the tissue. This does not allow for laser perforation through a thick tissue wall. Prolonged durations of the laser beam are required to penetrate the full thickness of the heart wall. This is especially pertinent to the hypertrophied heart. Prolonged exposure to the high energy of the laser beam exposes peripheral tissue to dangerously excessive thermal damage. Furthermore, controlled perforation in a rapidly beating heart may be impossible with prolonged durations of laser activation. It is also difficult to create a straight channel from the epicardium to the endocardium using the above technique in a beating heart.
Generally a large number of perforations are required. The epicardium must be reperforated for each channel created. But channels within the epicardium are usually inappropriate. In most conditions of ischemic heart disease, it is the endocardium, not the epicardium, which is deprived of a nutritive blood supply. In the above technique, the vaporization of the epicardium is incidental to providing the laser beam access to the endocardial tissue.
Although there are many different types of instruments used to focus a laser for surgical uses to date none of these implements are adaptable for use in transmyocardial revascularization. Many different devices have been used to provide for precise application of a laser beam in surgical applications including the combination of a laser beam with a laparoscope or in combination with an endoscope. These devices focus the laser beam slightly beyond the distal end of the operating channel of either the endoscope or the laparoscope and provide an intense laser beam at a precise location.
Another device used to apply a laser beam to a particular location is described in Davi U.S. Pat. No. 4,266,548. Davi discloses a surgical laser coupled with a hollow canula to direct a laser beam to tissue which is to be vaporized. This apparatus is used in the treatment of cardiac myopathies due to structural and functional abnormalities. In this application an incision is made in the heart to locate the area to be vaporized and provide access to the canula.
Clark U.S. Pat. No. 4,336,809 discloses a xenon ion laser which uses an optical needle to apply laser light to a desired area. The needle has a fiber optic core used to transmit the light to the desired region. Such fiber optic systems are presently incompatible with high intensity infrared lasers such as carbon dioxide lasers. Therefore, it is unsuitable for use when high intensity radiation is required.